The motor of an FRP (Fiber-Reinforced Plastic) spraying machine serves as the core power source, directly driving the spray gun and pump to deliver and atomize resin and hardener. Any motor failure will directly cause equipment shutdown. Due to the spraying environment, which is often characterized by resin dust, humidity, and vibration, motor failures are mainly concentrated in four categories: electrical connections, mechanical wear, poor heat dissipation, and overload. Troubleshooting should follow the principles: "first ensure power-off safety, then electrical before mechanical, external before internal." Repairs must be performed according to the fault type with professional operations to ensure the motor's performance is restored and meets explosion-proof, waterproof, and other on-site requirements.

I. Core Safety Preparations Before Troubleshooting

Power off and verify: Turn off the main power switch, pull down the knife switch, unplug the motor power plug, and use a voltage tester to confirm no residual voltage to prevent electric shock. If it is an explosion-proof motor, ensure there are no flammable resin vapors on site to avoid sparks during repair that could cause a fire hazard.

Clean the working environment: Remove resin dust, fiber debris, and oil stains from the motor surface to prevent dust from entering the motor or oil affecting electrical component testing. Organize the pipelines around the motor to avoid accidental damage to wiring.

Prepare specialized tools: Multimeter (for voltage and resistance), megohmmeter (for insulation resistance), screwdrivers, socket wrenches, motor puller, brush, insulating tape, lubricating oil (compatible with motor bearing model), etc., ensuring all tools are accurate and effective.

II. Common Fault Troubleshooting Process (Classified by Fault Symptom)

 (A) Motor does not start at all, no sound

Such faults are mostly due to power interruption, electrical connection failure, or burnt stator windings. Troubleshooting steps:

Check the power supply system: Use a multimeter to measure the output voltage at the power socket and main switch to confirm whether it meets the motor's rated voltage (e.g., 380V three-phase, 220V single-phase), and rule out voltage loss or undervoltage. Check whether the power cord is broken, frayed, or the plug is loose or oxidized; replace with a dedicated wear-resistant power cord if damaged.

Check control components: Check whether the emergency stop switch is reset, whether the thermal relay has tripped (press the reset button to attempt recovery), and whether the AC contactor is engaged (listen for engagement sound or measure contact continuity with a multimeter). If it is a variable frequency drive (VFD) controlled motor, check whether the VFD displays a fault code, and troubleshoot VFD parameter settings or internal faults.

Check the motor windings and terminal box: Open the motor terminal box and check whether the terminal blocks are loose, burnt, detached, or the terminal insulation is damaged. Use a megohmmeter to measure the insulation resistance of the motor stator windings to ground. If the resistance is less than 0.5MΩ, the winding insulation has broken down. Use a multimeter to measure the resistance of the three-phase windings. If the resistance of one phase is infinite, the winding is open-circuited. If the deviation among the three-phase resistances exceeds 5%, there is an inter-turn short circuit in the windings.

(B) Motor makes sound when starting but does not rotate, or trips immediately after starting

Such faults are mostly due to mechanical jamming, starting capacitor failure (single-phase motor), or phase loss operation. Troubleshooting steps:

Check for mechanical jamming (core): Disconnect the coupling between the motor and the spraying machine pump. Manually turn the motor shaft. If it cannot turn or the resistance is high, the fault lies in the mechanical part. Check: whether the motor bearings are dry, seized, or severely worn; whether the motor rotor is rubbing against the stator (bore rub); whether the impeller or pump body is jammed by solidified resin or fiber debris (requires joint inspection with the spraying machine transmission components).

Check for phase loss operation (three-phase motor): Use a multimeter to verify whether all three phases have voltage. Check whether one phase of the three-phase power cord is broken, or a terminal block in the terminal box is loose. Check whether one phase contact of the AC contactor is burnt or making poor contact. Phase loss operation can cause the motor windings to overheat and burn out; it must be prioritized.

Check the starting capacitor (single-phase motor): Observe whether the starting capacitor is bulging, leaking, or cracked. Use a multimeter to measure the capacitance. If the deviation from the rated value exceeds 20%, the capacitor has failed and must be replaced with the same type of explosion-proof capacitor.

(C) Motor starts but runs abnormally, with abnormal noise, vibration, or overheating

Such faults are mostly due to bearing wear, rotor imbalance, overload, or poor heat dissipation. Troubleshooting steps:

Identify the source of abnormal noise and vibration:
- If there is a dull "humming" noise accompanied by reduced speed, it is mostly overload. Check whether the spray gun nozzle is blocked, the pump pressure is too high, or the resin viscosity exceeds the motor's load capacity.
- If there is a "rustling" friction noise, it is mostly due to bearing wear or lack of oil, or rotor bore rub. Disassemble the motor to check the bearings and the clearance between stator and rotor.
- If there is a "clunking" impact noise, it is mostly due to rotor bar breakage, excessive coupling misalignment, or loose motor mounting bolts. Realign the coupling and tighten the mounting bolts.

Check for overheating: Touch the motor housing (after power off). If the temperature exceeds 70°C (158°F) or there is a burnt smell, check: whether the cooling fan is damaged or blocked, whether the motor cooling fins are covered with dust; whether the motor windings have a slight short circuit; or whether prolonged overload has caused winding overheating.

Check the rotor: If the motor speed fluctuates and load capacity drops, and electrical issues have been ruled out with a multimeter, it is likely rotor bar breakage. Use specialized instruments for detection or replace the rotor.

(D) Motor runs normally, but spraying machine power output is insufficient

Such faults are mostly due to a failure in the connection between the motor and the load, not the motor itself. Troubleshooting steps:

- Check whether the coupling is worn, cracked, the connecting bolts are loose, or the elastic pad is damaged.
- Check whether the motor pulley (if belt-driven) is slipping, or the belt is loose or aged.
- Confirm whether the motor speed meets the rated value. If it is a VFD motor, check whether the VFD output frequency is too low.

III. Corresponding Repair Methods (Professional Operating Procedures)

(A) Electrical fault repair

Terminal connection faults: Tighten loose terminal blocks with a screwdriver. Use sandpaper to remove oxidation from burnt terminals. If the terminal is damaged, replace with a terminal block of the same specification. For frayed power cords, wrap tightly with insulating tape or replace the entire cord. When wiring, strictly follow the "three-phase four-wire system" (ensure the ground protection wire is reliably connected).

Control component faults: Replace faulty thermal relays or AC contactors with the same model. If the VFD displays a fault code, consult the manual to troubleshoot—reprogram if parameters are incorrect, and contact a professional for internal faults.

Winding faults: For open circuit, short circuit, or insulation breakdown, the motor end cover and stator must be removed and rewound by a professional motor repair technician. After rewinding, vacuum impregnation and drying treatment are required to restore winding insulation. If the motor is severely burnt, it is recommended to replace it directly with an explosion-proof motor of the same power and model (suitable for FRP spraying environments).

(B) Mechanical fault repair

Bearing faults: Use a motor puller to remove the bearing from the motor shaft. Clean out old grease and debris. If the bearing balls are worn or the raceway is peeling, replace with a high-temperature-resistant, wear-resistant bearing of the same model. If the bearing is intact, apply an appropriate amount of lithium-based grease (fill to 1/2–2/3 of the bearing cavity). When installing, avoid striking the outer ring of the bearing to prevent damage.

Rotor bore rub: If caused by bearing wear leading to rotor misalignment, replacing the bearing will restore it. If caused by uneven stator-rotor clearance or rotor deformation, realign the rotor or replace the stator/rotor assembly to ensure the clearance meets motor technical standards.

Coupling/belt drive faults: Replace worn coupling elastic pads or broken couplings. Use a dial gauge to realign the coupling with a deviation ≤0.05mm. Adjust belt tension, replace aged or slipping belts, and tighten pulley mounting bolts.

(C) Load and heat dissipation fault repair

Overload: Clean solidified resin and debris from the spray gun nozzle and pump body. Reduce resin viscosity (by controlling resin temperature with a heater). Adjust the spraying machine pressure parameters to avoid prolonged motor overload.

Poor heat dissipation: Replace a damaged cooling fan. Clean dust and oil from cooling fins. If the ambient operating temperature is too high, add ventilation equipment to prevent the motor from running continuously in high-temperature environments.

IV. Post-Repair Acceptance and Daily Maintenance Points

Post-repair test run: After completing repairs, first perform a no-load test run for 30 minutes. Observe whether the motor speed is uniform, whether there is abnormal noise or vibration, and whether the housing temperature is normal. Use a multimeter to monitor whether voltage and current are stable (current not exceeding rated value). Then perform a load test run, connecting the spraying machine to test whether power output is sufficient. Only after confirming no faults should it be put into formal use.

Establish a maintenance log: Record in detail the fault symptoms, troubleshooting process, repair methods, and replaced part models to provide reference for future troubleshooting. Count the frequency of motor failures and analyze the root causes (e.g., dust, overload).

Daily preventive measures:
- Regularly clean dust from the motor surface, and check terminals and the cooling system monthly.
- Replenish grease for motor bearings every 3 months to avoid wear due to lack of lubrication.
- During operation, prevent the motor from contacting resin and hardener to avoid chemical corrosion of the motor housing and insulation.
- Never allow the motor to run overloaded for extended periods. Stop immediately and investigate if abnormal noise or overheating is detected.